1. Field of the Invention
The present invention relates to a filler cap for a fuel tank to seal a filler opening arranged to an automobile and so on.
2. Description of the Related Art
In the past, in a filler cap for a fuel tank of an internal-combustion engine arranged to an automobile and so on (such as an automobile, an agricultural machinery, a power generator, a lawn mower, a motor cycle, a boat and a ship, a construction machine, and a roadwork machine), there has been arranged an air passage channel to inhale an atmospheric air because it is necessary to inhale an atmospheric air the amount of which is in proportion to the volume of a fuel consumed in the fuel tank.
Accordingly, a vaporized gas generated from the fuel in the fuel tank is discharged into an atmosphere through the air passage channel arranged to the filler cap, thereby causing a problem of an environmental pollution. In addition, if the fuel tank arranged to an automobile and so on is tilted more than a prescribed angle, there has been a risk that the fuel leaks out through the air passage channel so that the fuel may catch fire.
In view of the foregoing, there has been proposed a technology to prevent large amount of the fuel in the fuel tank from leaking out through the air passage channel (see, Japanese Patent Laid-Open Publication No. H06-219461). That is, in this technology, a concavoconvex portion to form a winding passage channel that constitutes a part of the air passage channel is arranged in a gap between an outer cap and a receiving part of an inner cap in the filler cap described above; and, through this winding passage channel, only a harmful gas evaporated from the fuel in the fuel tank is discharged to outside the filler cap, while preventing a large amount of the fuel from leaking to outside by the concavoconvex portion.
In addition, to prevent the fuel in the fuel tank from leaking out through the air passage channel, a technology that a valve such as a ball valve and a float valve is arrange in the air passage channel is also conceivable.
Further, a technology by which a harmful gas evaporated from the fuel in the fuel tank is prevented from being discharged to an atmosphere has been proposed (see, Japanese Patent Laid-Open Publication No. H05-133287). That is, in this technology, a harmful gas evaporated from the fuel in the fuel tank is adsorbed onto an adsorbent member (activated carbon) arranged in a canister. Then, a harmful gas adsorbed onto the adsorbent member is desorbed, and then the harmful gas desorbed is inhaled through an induction pipe of an engine for burning; with this, the harmful gas evaporated from the fuel in the fuel tank was prevented from being discharged to an atmosphere through the air passage channel in the filler cap.